[RFI] Bonding to a PC

[Gedas]

Speaking of shielded cables I wanted to share something I have 
encountered on more then one occasion when I worked in the aerospace 
industry.

We had an issue with a product during some specialized radiated tests. 
Tasked with the investigation I found that the item was using shielded 
USB cables, as expected, the only problem was the maker of the cables (a 
large company that starts with an L and ends with a com) was not 
terminating the cable shield in any way. What was more disturbing to me 
was that I had to explain to two of their engineers that the shield had 
to be properly terminated to do any good. Just because it has a shield 
or braid around the conductors means absolutely nothing.

So, just because a cable says "shielded" do not assume it is properly 
terminated on both ends.

Gedas, W8BYA

Gallery at http://w8bya.com
Light travels faster than sound....
This is why some people appear bright until you hear them speak.

On 2/28/2019 5:12 PM, Jim Brown wrote:
> On 2/28/2019 11:34 AM, N4ZR wrote:
>> I want to try to manage RFI in my shack, among other things, by 
>> bonding all chassis together, including my shack computer, but the 
>> question has come up - where can I find chassis ground on a PC 
>> without serial or parallel ports? Is there a design standard, such as 
>> connecting the power supply chassis to ground buses on the 
>> motherboard, that makes this easy or does it have to be figured out 
>> PC by PC? 
>
> Bonding should always be to the shielding enclosure (chassis) if there 
> is one, and this is the required connection point for the Green wire. 
> DB-connectors are sometimes bonded, so consider the VGA connector (if 
> there is one). To make that connection to my laptops, I solder a short 
> bonding conductor to a lug small enough to fit under the retaining 
> screw for the DB connector, with a single Power Pole on the other end.
>
> If your PC only has USB ports, try making the connection to the shell 
> of one of them by sacrificing a USB cable like one of these.
>
> https://www.amazon.com/Cable-Matters-USB-Black-Feet/dp/B00C7RXR72
>
> USB is carried on twisted pairs, and cheap cables are often 
> unshielded.  If you're experiencing RFI, using shielded cables might 
> help.
>
> 73, Jim K9YC
>
>
>
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